You can change a bill of materials on an assembly item, replacing the current items with new items, then build the assembly. You will have to edit the items bill of materials every time you change the components of the items build. 

You must have Sage 50 Quantum if you want to use the same Assembly Item ID.  It is the only version that allows the user to revise the items used in the assembly.  

If you don't have Sage 50 Quantum, would you like a quote to upgrade? 

Yes, it is possible to use different materials to create an assembly with the same ID. In manufacturing or assembly processes, the assembly ID typically refers to a specific product or item that is composed of multiple components or parts.